The application of x-ray diffraction (XRD) to the measurement of residual stress and/or elastic strain is a known technique. The application of XRD to the measurement of phase composition (retained austenite) is more widespread than that of stress and strain measurement and has been described in the literature. Laboratory instrumentation capable of sequentially measuring both of these characteristics have been developed. However, until now no laboratory or portable XRD instrument was capable of measuring both characteristics simultaneously. The remainder of this background section will focus upon residual stress and phase composition (retained austenite) measurement in steels.